The invention relates to a fuse component with a fusible conductor, which extends within a gas filled cavity in a cylindrical tube between two end surfaces of the tube, two end caps of an electrically conductive material being applied to the two ends of the tube such that a respective electrical contact with the fusible conductor is produced. The invention further relates to a method of manufacturing such a fuse component.
Tubular fuse components of the type referred to above have been known for a long time. There are, for instance, fuse components, in which the cylindrical tube consists of a ceramic material and has a circular cylindrical internal cavity and a rectangular outer contour with rounded edges. The fusible conductor is, for instance, a wire, which extends diagonally within the cavity such that it contacts the walls of the tube merely at its ends. The wire of the fusible conductor is passed around the end surfaces of the tube, whereby the ends of the fusible conductor wire engage the external walls of the tube. Metallic end caps are placed on the two ends of the tube. The end caps can, for instance, be of an elastic material and pressed on to the ends of the tube, whereby the pressing on process ensures not only a firm fit of the end cap but also electrical contact with the fusible conductor. The metal caps can also be secured to the ends of the tube by adhesive or, after appropriate preparation of the surface of the outer wall of the tube, soldered to it. A number of techniques are known for applying the end caps which ensure not only a firm fit of the caps but also good electrical contact with the fusible conductor.
There are fuse components of the type referred to above, in which a gap remains between the end caps and the wall of the tube such that the interior of the tube is connected to the surroundings of the tube via the gap. In this event, there is a gas exchange between the cavity and the surroundings. In the event of heating and expansion of the gas in the cavity, it flows out of the cavity so that a relatively rapid pressure balance occurs.
There are additionally fuse components, in which the caps are so applied to the end of the tube that the cavity is hermetically sealed. With these components, the cavity can be filled with air or with a special gas (for instance nitrogen) under normal pressure or reduced pressure.
If the fusible conductor in the interior of the tube is ruptured (blows; i.e., the fuse cuts out), an arc generally forms. The impulsive energy supply as a result of the arc heats the gas optionally present in the cavity and the materials which vaporize when blowing occurs. With a fuse component with a hermetically sealed cavity and an air or gas filling, the energy supplied by the arc results in a sudden, step increase in the pressure in the cavity of the fuse component. This pressure pulse has a quenching action on the arc and is thus desirable.
Of disadvantage, however, with a fuse component with a hermetically sealed cavity is the fact that the pressure increase in the cavity is also produced if the fuse component is heated from the exterior, for instance in the manufacturing process. Such heating occurs, for instance, when the end caps are briefly brought to a relatively high temperature to produce a solder connection between the ends of the fusible conductor and the positioned, metallic end caps. A temperature increase can also occur during a curing process of an adhesive, which is to connect the end caps to the tube. The pressure increase, associated with such heating, in the interior of the tube results in an undesired loading of the fuse component and possibly in the formation of a pressure balancing passage (capillary passage) between the cavity in the tube and the surroundings through the gap between the tube and the end cap. The formation of such an undesired capillary adjacent to the fusible conductor was determined, for instance, in fuse components which are sealed in their end regions with a pourable silicone.
It is therefore the object of the invention to provide a fuse component of the type referred to above, whose interior is hermetically sealed, in operation, but in which the problems of the type referred to above occurring in the event of sudden temperature and pressure increases during manufacture of the component are avoided.
This object is solved by a fuse component with the features of claim 1. The object is also solved by a method of manufacturing a fuse component with the features of claim 10.